According to a manufacturing method of a secondary battery that has been proposed conventionally (refer to JP2004-342520A), it is possible to certainly perform degassing, after conditioning and the like, of the secondary battery having an exterior body formed by a thin and lightweight exterior film, such as a laminate film, and to sufficiently secure sealability after the degassing.
This includes an enclosing process that encloses a power generation element in the exterior body by joining an opening part of the exterior film while forming an unjoined part that communicates with the inside and that is separated from the outside, a degassing process that forms a degassing hole while limiting the thickness of the unjoined part to the predetermined thickness or less, and a second sealing process that encloses the power generation element by joining the unjoined part. As a method of suppressing swelling of the unjoined part and relaxing stress concentration, the thickness of the unjoined part is controlled when an internal pressure of the exterior body is high. This prevents the unjoined part from returning to its original shape at the time of joining, as the large swelling or deformation is caused at the unjoined part due to the increase in the internal pressure by generated gas, and prevents a part of the joined part from being separated, as the stress concentrates in the vicinity of the unjoined part due to the swelling of the unjoined part.